Chapter 9: Central Nervous System Flashcards

1
Q

two divisions of the nervous system

A

1) central nervous system
- brain and spinal cord
- is the integrating centre
2) peripheral nervous system
- all neural tissue outside of the CNS

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what are neurons?

A

neurons are cells that send and receive electrical signals rapidly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

role of central nervous system

A
  • consists of the spinal cord and the brain
  • integrates information from internal/external environment to illicit appropriate responses for the maintenance of homeostasis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

role of peripheral nervous system

A
  • includes all neural tissue outside the CNS
  • provides communication between the CNS and the rest of the body
  • has two divisions: somatic and autonomic
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is CSF and why is it important?

A
  • cerebrospinal fluid is a clear watery fluid that bathes the brain and spinal cord (the CNS)
  • it is important because it helps with protection, nourishment, and waste removal in the brain
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

main functions of CSF

A
  • CSF cushions the brain (acts as a shock absorber) by preventing the soft nervous tissue from colliding with the hard skull
  • CSF helps maintains a stable interstitial fluid environment because it provides neurons and glial cells with essential nutrients and helps with removal of waste products
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

where does CSF come from?

A
  • it is secreted by the ependymal cells of the ventricles in brain
  • CSF is then circulated throughout the four ventricles
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

how much blood supply is sent to the brain? why so much?

A
  • the CNS receives 15% of the blood that the heart pumps
  • a large blood supply is necessary because the CNS tissue has a high rate of metabolic activity compared to most other body tissues
  • therefore, it has a high demand for glucose and oxygen to meet its energy needs
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what happens if there inadequate blood flow to the brain?

A
  • can result in irreversible damage to CNS tissue
  • can cause deficits in certain functions like the ability to speak or move an arm
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

why is blood flow to the brain critical?

A
  • to help meet the brains energy requirements
  • blood flow provides oxygen and glucose to the brain which is needed needs to function properly and stay alive
  • neurons in CNS depend on aerobic glycolysis (which requires oxygen and glucose) to maintain ATP levels therefore requiring a steady supply from the blood
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what are the different energy supplies to the brain?

A
  • GLUCOSE and oxygen are the main energy supply
  • ketones can be used for energy during extreme conditions when glucose supply is limited
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

why is the CNS so sensitive to changes in blood supply?

A

it is because the brain and spinal cord have high metabolic demands and limited energy reserves.

  • the brain has limited glycogen stores so cells in the CNS must obtain glucose directly from the blood instead
  • cells in the CNS do not have access to fatty acids reserves for energy, which increases their demand for glucose
  • neurons are more sensitive to oxygen deprivation than other kinds of cells with lower rates of metabolism (because they cannot perform anaeorbic glycolysis)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what are capillaries?

A
  • they are the site of exchange between blood and interstitial fluid
  • they’re composed of a thin, single layer of endothelial cells (a type of epithelial cell)
  • small wall = short diffusion distance for exchange
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is blood-brain barrier?

A
  • a physical barrier that is selectively permeable
  • the capillaries in the brain create protective barrier that restricts the exchange of solutes between blood and brain
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

how does the blood brain barrier work?

A
  • barrier is the result of tight junctions between capillary endothelial cells
  • they eliminate capillary pores which restricts the diffusion of molecules between the cells
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

why are astrocytes important to the formation of the blood-brain barrier?

A
  • they stimulate endothelial by releasing chemical signals that promote the formation of tight junctions between the endothelial cells of the brain’s blood vessels
17
Q

importance of the blood-brain barrier

A
  • protects the CNS from harmful substances that may be present in the blood by restricting movement of molecules from the blood stream to the brain
  • in order to move across the barrier (enter or leave capillaries) the molecules must cross the endothelial cells themselves.
18
Q

what is the spinal cord?

A
  • a cylinder of nervous tissue
  • is continuous with the lower end of the brain and is surrounded by the vertebral column
  • is the origin of spinal nerves (31 pairs)
19
Q

what is organization of white and gray matter in the spinal cord?

A

gray matter = concentrated within a butterfly-shaped region in the middle of the cord
white matter = found in the surrounding outer region

20
Q

what is organization and role of gray matter in the spinal cord?

A
  • divided into dorsal (posterior) and ventral (anterior) regions
  • dorsal region = sensory functions / afferent
    –> afferent neurons originate in the periphery as sensory receptors and terminate in the dorsal horn
  • ventral region = motor functions / efferent
    –> efferent neurons originate in the ventral horn and travel to the periphery, where they form synapses with skeletal muscles
21
Q

what is organization and role of white matter in the spinal cord?

A
  • white matter of the spinal cord form tracts that provide communication between the brain and spinal cord
    –> ascending tracts = transmit information from spinal cord to brain
    –> descending tracts = transmit information from brain to spinal cord
22
Q

what is a reflex?

A

an automatic, patterned response to a sensory stimulus

23
Q

what is a reflex arc?

A
  • a neural pathways for reflexes
24
Q

3 reflex pathways

A

1) stretch reflex (i.e knee jerk)
2) withdrawal reflex
3) crossed-extensor Reflexes

25
Q

5 components of a reflex arc

A

1) sensory receptor
2) an afferent neuron
3) integrating centre
4) an efferent neuron
5) an effector organ

26
Q

how does the reflex arc work?

A
  • the receptor first detects a stimulus
  • information is then transmitted from the receptor to the CNS via the afferent neuron
  • the CNS, which functions as the integrator, sends signals via the efferent neuron
  • the efferent neuron transmits signals to the effector organ which stimulates it to produce a specific response.

–>the integration can consist of a single neuron or a network of neurons

27
Q

4 classifications of reflexes

A

1) spinal or cranial
–> based on the level of neural processing involved
2) somatic or autonomic
–> depends on which efferent division controls the pathway
3) innate or conditioned
–> whether you’re born with the reflex or learned through experiences
4) monosynaptic or polysynaptic
–> monosynaptic reflexes = the neural pathway consists of only twoneurons and a single synapse
–> polysynaptic reflexes = contain more than two neurons and multiple synapses

28
Q

what is the muscle spindle stretch reflex?

A

a rapid and automatic response to changes in muscle length

29
Q

how does the stretch reflex work using the knee-jerk test?

A
  • tapping the patellar tendon below the kneecap stretches the quadricep muscle. this causes a change in muscle fibre length.
  • muscle spindles (which are sensory receptors) the muscle detect a change and get excited
  • this triggers action potentials to travel in afferent neurons to the spinal cord (acting as an integration center)
  • in the spinal cord, the afferent neurons make direct excitatory synaptic connections with efferent neurons that innervate the quadriceps muscle
  • this stimulates the quadriceps to contract and the leg to “kick” forward
  • the afferent neurons also synapse with inhibitory interneurons that innervate hamstring motor neurons allowing it to relax
30
Q

what is a withdrawal reflex?

A

when a portion of the body is subjected to a painful stimulus, it withdraws from the stimulus automatically

31
Q

what is the crossed-extensor reflex?

A

a contralateral reflex, meaning the reflex occurs on the opposite side of the body from the stimulus

32
Q

how does the withdrawal reflex work?

A
  • begins when specialized sensory receptors, such as pain receptors (nociceptors) in the skin, detect a harmful or painful stimulus
  • the sensory/ afferent neurons transmit signals from the site of the stimulus to the spinal cord (integrating centre).
  • the sensory/ afferent neurons enter the spinal cord and have an excitatory synapse with interneurons.
  • the interneurons in the spinal cord excite and relay signals to the motor/efferent neurons that innervate the skeletal muscles that cause withdrawal of the limb
  • these motor neurons stimulate the contraction in the affected limb.
  • the contraction pulls the limb away from the harmful stimulus, allowing for a rapid and protective withdrawal.
  • to facilitate the withdrawal, there is often a simultaneous relaxation of antagonistic muscles (those opposing the action), allowing for a quick and coordinated movement.
33
Q

how does the crossed-extensor reflex work?

A
  • begins with the detection of a painful stimulus in one limb which activates pain receptors (nociceptors) in the affected area
  • sensory/ afferent neurons carry the pain signals from the stimulated limb to the spinal cord (integrating centre) where they synapse with interneurons.
  • the interneurons have branches that can relay signals to motor/efferent neurons on both sides of the spinal cord which creates a coordinated response involving both the stimulated and opposite limbs.
  • on the side where the painful stimulus occurs, motor/efferent neurons signal the muscles to contract (withdrawal reflex). This causes the withdrawal of the limb from the stimulus.
  • simultaneously, on the opposite side of the body, motor/efferent neurons stimulate muscles to extend which helps support the body’s weight and maintain balance during the withdrawal of the other limb.